1. Field of the Invention
This invention relates to a liquid jet recording head which ejects liquid to produce flying liquid droplets to record.
2. Description of the Prior Art
Ink jet recording methods (liquid jet recording methods) have recently attracted attention since noise upon recording is very little and a high speed recording is possible, and further, the recording can be made on plain paper without any special treatment such as fixation
Among them, for example, a liquid jet recording method disclosed in Japanese Patent Laid-open No. 51837/1979 and German Patent Laid-open (DOLS)No. 2843064 is different from other liquid jet recording methods in point that heat energy is applied to liquid to produce a driving force for ejecting liquid droplets.
That is, the above-mentioned recording method comprises applying heat energy to a liquid to cause an abrupt increase in the volume of the liquid, ejecting the liquid from the orifice at the front of the recording head to form flying liquid drop.ets and attaching the droplets to a record receiving member to effect recording.
In particular, the liquid jet recording method disclosed in DOLS No. 2843064 cannot be only effectively suitable for so-called "drop-on demand" recording methods, but also enables to realize easily a high density multiorifice recording head of a full-line type, and therefore, images of high resolution and high quality can be produced at a high speed.
The recording head portion of an apparatus used for the above-mentioned recording method comprises a liquid ejecting portion constituted of an orifice for ejecting liquid and a liquid flow path containing, as a part of the construction, a heat actuating portion communicated with the orifice and applying heat energy for ejecting liquid droplets to the liquid, and an electrothermal transducer for generating heat energy.
The electrothermal transducer is provided with a pair of electrodes formed on a support and a resistive heater layer connected to the electrodes and having a region generating heat (heat generating portion) between the electrodes.
A typical embodiment of the structure of such liquid jet recording head is shown in FIG. 1A and FIG. 1B.
FIG. 1A is a partial front view of the liquid jet recording head viewed from the orifice side, and FIG. 1B is a partial cross-sectional view taken along the dot and dash line XY of FIG. 1A.
Recording head 100 is constituted of orifice 104 and liquid ejecting portion 105 formed by bonding the surface of substrate 102 provided with electrothermal transducer to a grooved plate 103 having a predetermined number of grooves having a predetermined width and depth at a predetermined line density such that the grooved plate covers the substrate In FIG. 1, the recording head has a plurality of orifices 104, but the present invention is not limited to such an embodiment and a recording head having a single orifice is also within the scope of the present invention.
Liquid ejecting portion 105 has orifice 104 ejecting liquid at the end and heat acturating portion 106 where heat energy generated by electrothermal transducer is applied to liquid to form a bubble and an abrupt state change due to expansion and shrinkage of the volume occurs.
Heat actuating portion 106 is located above heat generating portion 107 of electrothermal transducer and a heat actuating surface 108 where heat generating portion 107 contacts the liquid is the bottom surface of the heat actuating portion 106.
Heat generating portion 107 is constituted of resistive heater layer 110 provided on lower layer 109 formed in substrate and upper layer 111 provided on resistive heater layer 110. Electrodes 112 and 113 are provided on the surface of resistive heater layer 110 for flowing electric current to the layer 110 to generate heat. Electrode 113 is a selection electrode for selecting the heat generating portion of each liquid ejecting portion to generate heat, and electrode 112 is an electrode common to heat generating portions of liquid ejecting portions and is provided along the liquid flow path of each liquid ejecting portion.
Upper layer 111 serves to protect chemically and physically resistive heater layer 110 from the liquid at the heat generating portion 107 by isolating resistive heater layer 110 from the liquid in the liquid flow path at liquid ejecting portion 105 and further upper layer 111 prevents electrodes 112 and 113 from shortcircuiting through the liquid. Thus, upper layer 111 serves to protect resistive heater layer 110. Upper layer 111 also serves to prevent electric leakage between adjacent electrodes. In particular, it is important to prevent electric leakage between selection electrodes and electrolytic corrosion of electrodes caused by electric current flowing in an electrode resulting from contact of an electrode under the liquid flow path with the liquid which happens by some cause. Therefore, such an upper layer 111 having a protective function is provided on at least an electrode which is disposed under a liquid flow path.
The upper layer is required to have various properties depending on the position to be disposed. That is, for example, the following characteristics are required at heat generating portion 107:
(1) heat resistance, PA1 (2) liquid resistance, PA1 (3) liquid penetration preventing property, PA1 (4) thermal conductivity, PA1 (5) oxidation preventing property, PA1 (6) insulating property, and PA1 (7) breakage preventing property.
At portions other than heat generating portion 107, sufficiently high liquid penetration preventing property, liquid resistance and breakage preventing property are required though the resisting property to thermal conditions is not required to be so good.
However, at present there is not any material for constituting the upper layer capable of sufficiently satisfying all the characteristics (1)-(7) as mentioned above. It is the present status that some of the conditions (1)-(7) are not severely requested.
Apart from the above, in the case of a liquid jet recording head of a multi-orifice type, since a number of fine electrothermal transducers are formed on the substrate simultaneously, formation of each layer of the substrate and removal of a part of the formed layer are repeated, and as a result, the surface on which each layer in the upper layer is to be formed becomes a fine uneven surface having step edge portions, and therefore, the step coverage property of the layers in the upper layer at the step edge portions becomes important. In other words, when the step coverage property at the step edge portions is poor, penetration of the liquid occurs at the portions and causes electrolytic corrosion or dielectric breakdown. Further, when the formed upper layer suffers the formation of defects upon fabrication with a considerable probability, penetration of liquid occurs through the defect portion resulting in shortening the life of the electrothermal transducer to a great extent.
In view of the foregoing, it is required that the upper layer has a good step coverage property at the step edge, defects such as pinholes and the like occur in the formed layer with only a low probability and even if the defects are formed, the number of defects is negligibly small or less.
In order to satisfy those requisites, heretofore the upper layer has been produced by laminating the first protective layer composed of an inorganic insulating material and the second protective layer composed of an organic material, or the first protective layer is constituted of two layers, that is, an under layer composed of an inorganic insulating material and an above layer composed of an inorganic material of high toughness, relatively excellent mechanical strength and having adhesion and cohesion to the first protective layer and the second protective layer, such as metals and the like, or the third protective layer composed of an inorganic material such as metals and the like overlies the second protective layer.
However, it is very difficult that the upper layer having no defects is formed by the above-mentioned process. The liquid jet recording head satisfying all the requirements and having totally excellent durability for use has not yet been provided